Getting Input for a Macro

The dialog-based macro discussed in Chapter 14, A Dialog-Based Macro reflects a conventional approach to obtaining input in a Java program. Nevertheless, it can be too lengthy or tedious for someone trying to write a macro quickly. Not every macro needs a user interface specified in such detail; some macros require only a single keystroke or no input at all. In this section we outline some other techniques for obtaining input that will help you write macros quickly.

Getting a Single Line of Text

As mentioned earlier in the section called “Helpful Methods in the Macros Class”, the method Macros.input() offers a convenient way to obtain a single line of text input. Here is an example that inserts a pair of HTML markup tags specified by the user.

// Insert_Tag.bsh

void insertTag()
    caret = textArea.getCaretPosition();
    tag = Macros.input(view, Enter name of tag:);
    if( tag == null || tag.length() == 0) return;
    text = textArea.getSelectedText();
    if(text == null) text = ;
    sb = new StringBuffer();
    if(text.length() == 0)
        textArea.setCaretPosition(caret + tag.length() + 2);


// end Insert_Tag.bsh

Here the call to Macros.input() seeks the name of the markup tag. This method sets the message box title to a fixed string, Macro input, but the specific message Enter name of tag provides all the information necessary. The return value tag must be tested to see if it is null. This would occur if the user presses the Cancel button or closes the dialog window displayed by Macros.input().

Getting Multiple Data Items

If more than one item of input is needed, a succession of calls to Macros.input() is a possible, but awkward approach, because it would not be possible to correct early input after the corresponding message box is dismissed. Where more is required, but a full dialog layout is either unnecessary or too much work, the Java method JOptionPane.showConfirmDialog() is available. The version to use has the following prototype:

  • public static int showConfirmDialog(Component parentComponent,
     Object message,
     String title,
     int optionType,
     int messageType);

The usefulness of this method arises from the fact that the message parameter can be an object of any Java class (since all classes are derived from Object), or any array of objects. The following example shows how this feature can be used.

// excerpt from Write_File_Header.bsh

title = Write file header;

currentName = buffer.getName();

nameField = new JTextField(currentName);
authorField = new JTextField(Your name here);
descField = new JTextField(, 25);

namePanel = new JPanel(new GridLayout(1, 2));
nameLabel = new JLabel(Name of file:, SwingConstants.LEFT);
saveField = new JCheckBox(Save file when done,

message = new Object[9];
message[0] = namePanel;
message[1] = nameField;
message[2] = Box.createVerticalStrut(10);
message[3] = Author's name:;
message[4] = authorField;
message[5] = Box.createVerticalStrut(10);
message[6] = Enter description:;
message[7] = descField;
message[8] = Box.createVerticalStrut(5);

if( JOptionPane.OK_OPTION !=
    JOptionPane.showConfirmDialog(view, message, title,
    return null;

// *****remainder of macro script omitted*****

// end excerpt from Write_File_Header.bsh

This macro takes several items of user input and produces a formatted file header at the beginning of the buffer. The full macro is included in the set of macros installed by jEdit. There are a number of input features of this excerpt worth noting.

  • The macro uses a total of seven visible components. Two of them are created behind the scenes by showConfirmDialog(), the rest are made by the macro. To arrange them, the script creates an array of Object objects and assigns components to each location in the array. This translates to a fixed, top-to-bottom arrangement in the message box created by showConfirmDialog().

  • The macro uses JTextField objects to obtain most of the input data. The fields nameField and authorField are created with constructors that take the initial, default text to be displayed in the field as a parameter. When the message box is displayed, the default text will appear and can be altered or deleted by the user.

  • The text field descField uses an empty string for its initial value. The second parameter in its constructor sets the width of the text field component, expressed as the number of characters of average width. When showConfirmDialog() prepares the layout of the message box, it sets the width wide enough to accommodate the designated with of descField. This technique produces a message box and input text fields that are wide enough for your data with one line of code.

  • The displayed message box includes a JCheckBox component that determines whether the buffer will be saved to disk immediately after the file header is written. To conserve space in the message box, we want to display the check box to the right of the label Name of file:. To do that, we create a JPanel object and populate it with the label and the checkbox in a left-to-right GridLayout. The JPanel containing the two components is then added to the beginning of message array.

  • The two visible components created by showConfirmDialog() appear at positions 3 and 6 of the message array. Only the text is required; they are rendered as text labels.

  • There are three invisible components created by showConfirmDialog(). Each of them involves a call to Box.createVerticalStrut(). The Box class is a sophisticated layout class that gives the user great flexibility in sizing and positioning components. Here we use a static method of the Box class that produces a vertical strut. This is a transparent component whose width expands to fill its parent component (in this case, the message box). The single parameter indicates the height of the strut in pixels. The last call to createVerticalStrut() separates the description text field from the OK and Cancel buttons that are automatically added by showConfirmDialog().

  • Finally, the call to showConfirmDialog() uses defined constants for the option type and the message type. The constants are the same as those used with the Macros.confirm() method; see the section called “Helpful Methods in the Macros Class”. The option type signifies the use of OK and Cancel buttons. The QUERY_MESSAGE message type causes the message box to display a question mark icon.

    The return value of the method is tested against the value OK_OPTION. If the return value is something else (because the Cancel button was pressed or because the message box window was closed without a button press), a null value is returned to a calling function, signaling that the user canceled macro execution. If the return value is OK_OPTION, each of the input components can yield their contents for further processing by calls to JTextField.getText() (or, in the case of the check box, JCheckBox.isSelected()).

Selecting Input From a List

Another useful way to get user input for a macro is to use a combo box containing a number of pre-set options. If this is the only input required, one of the versions of showInputDialog() in the JOptionPane class provides a shortcut. Here is its prototype:

  • public static Object showInputDialog(Component parentComponent,
     Object message,
     String title,
     int messageType,
     Icon icon,
     Object[] selectionValues,
     Object initialSelectionValue);

This method creates a message box containing a drop-down list of the options specified in the method's parameters, along with OK and Cancel buttons. Compared to showConfirmDialog(), this method lacks an optionType parameter and has three additional parameters: an icon to display in the dialog (which can be set to null), an array of selectionValues objects, and a reference to one of the options as the initialSelectionValue to be displayed. In addition, instead of returning an int representing the user's action, showInputDialog() returns the Object corresponding to the user's selection, or null if the selection is canceled.

The following macro fragment illustrates the use of this method.

// fragment illustrating use of showInputDialog()
options = new Object[5];
options[0] = "JLabel";
options[1] = "JTextField";
options[2] = "JCheckBox";
options[3] = "HistoryTextField";
options[4} = "-- other --";

result = JOptionPane.showInputDialog(view,
    "Choose component class",
    "Select class for input component",
    null, options, options[0]);

The return value result will contain either the String object representing the selected text item or null representing no selection. Any further use of this fragment would have to test the value of result and likely exit from the macro if the value equaled null.

A set of options can be similarly placed in a JComboBox component created as part of a larger dialog or showMessageDialog() layout. Here are some code fragments showing this approach:

// fragments from Display_Abbreviations.bsh
// import statements and other code omitted

// from main routine, this method call returns an array
// of Strings representing the names of abbreviation sets

abbrevSets = getActiveSets();


// from showAbbrevs() method

combo = new JComboBox(abbrevSets);
// set width to uniform size regardless of combobox contents
Dimension dim = combo.getPreferredSize();
dim.width = Math.max(dim.width, 120);
combo.setSelectedItem(STARTING_SET); // defined as "global"

// end fragments

Using a Single Keypress as Input

Some macros may choose to emulate the style of character-based text editors such as emacs or vi. They will require only a single keypress as input that would be handled by the macro but not displayed on the screen. If the keypress corresponds to a character value, jEdit can pass that value as a parameter to a BeanShell script.

The jEdit class InputHandler is an abstract class that that manages associations between keyboard input and editing actions, along with the recording of macros. Keyboard input in jEdit is normally managed by the derived class DefaultInputHandler. One of the methods in the InputHandler class handles input from a single keypress:

  • public void readNextChar(String prompt,
     String code);

When this method is called, the contents of the prompt parameter is shown in the view's status bar. The method then waits for a key press, after which the contents of the code parameter will be run as a BeanShell script, with one important modification. Each time the string __char__ appears in the parameter script, it will be substituted by the character pressed. The key press is consumed by readNextChar(). It will not be displayed on the screen or otherwise processed by jEdit.

Using readNextChar() requires a macro within the macro, formatted as a single, potentially lengthy string literal. The following macro illustrates this technique. It selects a line of text from the current caret position to the first occurrence of the character next typed by the user. If the character does not appear on the line, no new selection occurs and the display remains unchanged.

// Next_Char.bsh

script = new StringBuffer(512);
script.append( "start = textArea.getCaretPosition();"         );
script.append( "line = textArea.getCaretLine();"              );
script.append( "end = textArea.getLineEndOffset(line) + 1;"   );
script.append( "text = buffer.getText(start, end - start);"   );
script.append( "match = text.indexOf(__char__, 1);"           );
script.append( "if(match != -1) {"                            );
script.append(   "if(__char__ != '\\n') ++match;"             );
script.append(   ", start + match - 1);" );
script.append( "}"                                            );

view.getInputHandler().readNextChar("Enter a character",

// end Next_Char.bsh

Once again, here are a few comments on the macro's design.

  • A StringBuffer object is used for efficiency; it obviates multiple creation of fixed-length String objects. The parameter to the constructor of script specifies the initial size of the buffer that will receive the contents of the child script.

  • Besides the quoting of the script code, the formatting of the macro is entirely optional but (hopefully) makes it easier to read.

  • It is important that the child script be self-contained. It does not run in the same namespace as the parent macro Next_Char.bsh and therefore does not share variables, methods, or scripted objects defined in the parent macro.

  • Finally, access to the InputHandler object used by jEdit is available by calling getInputHandler() on the current view.